Anonymous class Dan's Mock exam

[Reddy Yeluru]

Referring to the following code below, the out put is 5. I am showing the flow here with the numbers as I understood. When I debug this code using IntelliJ, I could not follow the flow. Can any body clarify me if am wrong of if I am missing any thing.

abstract class A {
  private int x = 4;                        //3
  private int y = 2;                        //4 
  public A(int i1) {                        //2
     x=i1;}                                 //5
  public int x() {return x;}                //10 
  public void x(int x) {this.x = x;}        
  public int y() {return y;}                //11
  public void y(int y) {this.y = y;}
  public void incY() {y++;}                 //7
  public abstract int math();
}
class B {
  static A a1 = new A(2) {                 //1
    {incY();}                              //6
    public int math() {return x()+y();}    //9
  };
  public static void main(String[] args) {
    System.out.print(a1.math());           //8 
  }
}

Thankx in advance,

[Steve Lovelace]

Seems like you negotiatied the tricky part perfectly, then slipped on the arithmetic? By your numbers:

4: y = 2

5: x = 2

7: y++

9: x + y

[Dep Joy]

I have another question,
new A(2) {
{incY();}
//... code skipped
};
here how could the statements {incY();} compiled(though it does)? I understand only static method could be used this way, but it not declared as static, please enlighten me, thanks!

[Steve Lovelace]

I assume you mean you know about static initializers. Instance initializers are there too, and the above is an example (does make you look twice though, doesn't it?).

[Dep Joy]

Thank Steve, is this instance initializer on the SCJP objective list? As far as I can remember, it is not mentioned in both K&B and RHE which two books I have.
[ September 19, 2003: Message edited by: Dep Joy ]

[Steve Lovelace]

Right, I don't remember it mentioned in K&B, which is what I'm relying on, nor do I recall it popping up anywhere else but in this question. Might be a safe bet to ignore, but on the other hand, there's nothing to it. When a new instance is being initialized, after all its superclass initializations have completed: 1) its instance vars are initialized 2) any instance initializers are run 3) the constructor is run.

[Barkat Mardhani]

posted by Steve:

Right, I don't remember it mentioned in K&B, which is what I'm relying on, nor do I recall it popping up anywhere else but in this question. Might be a safe bet to ignore, but on the other hand, there's nothing to it. When a new instance is being initialized, after all its superclass initializations have completed: 1) its instance vars are initialized 2) any instance initializers are run 3) the constructor is run.

Hi Steve:
I thought it was done in textual order. Following will give forward reference error:

class Test{
int y;
{y = x;}
int x = 2;
public static void main(String[] args) {
new Test();
}
}  

[Steve Lovelace]

Didn't know that! Thanks!